The present invention generally relates to optical semiconductor devices, and more particularly to a semiconductor optical bandpass filter that selectively passes an optical beam of a specified wavelength.
Various optical elements are needed in the optical telecommunication systems such as laser diodes, photodetectors and optical filters. Among others, the optical filters are the essential elements in the large capacity optical telecommunication network that employs the technique of wavelength multiplexing. In the wavelength multiplex network, a large number of information signals are multiplexed on a single optical fiber by changing the frequency and hence the wavelength of the optical carrier for each optical channel. In such a system, a very large number of optical filters, each having its own passband and a central passband wavelength, are needed in order to demultiplex the optical signals or to switch the connection of the optical channels.
Conventionally, the optical filters for use in the optical telecommunication network have been formed based upon a multi-layer mirror or a Fabry-Perot resonator. In such conventional filters, the passband wavelength has been determined by the construction of the filter such as the geometrical dimension or the composition of the material. Thereby, one has to provide a large number of filters in correspondence to the signal channels of the telecommunication system, together with a distribution network for distributing the optical signals to each of these filters. When the number of the optical channels is increased, such a construction becomes inevitably bulky and expensive.